''Cratochelone'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerh ...

in the family

Protostegidae Protostegidae is a family of extinct sea turtle, marine turtles that lived during the Cretaceous period. The family includes some of the largest sea turtles that ever existed. The largest ''Archelon'' had a head long. Like most sea turtles, the ...

and containing a single species ''Cratochelone berneyi''. The species is known only from the mid to late Albian Toolebuc Formation, part of the Rolling Downs Group, in the Hughenden of Central northern

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

, Australia.

History and classification

''Cratochelone berneyi'' is known only from one fossil, the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

, specimen number "QM F14550". The specimen is composed of a grouping of disassociated post-cranial skeleton elements in a hard, fine-grained and "dirty-stone colored" sedimentary matrix. The bones include portions of the left side

plastron The turtle shell is a shield for the ventral and dorsal parts of turtles (the Order (biology), order Testudines), completely enclosing all the turtle's vital organs and in some cases even the head. It is constructed of modified bony elements such ...

, the shoulder girdle, and segments of a forelimb. The fossil is thought to have been recovered by F. L. Berney from outcrops of the Toolebuc Formation exposed in the Eromanga Basin. The type specimen is currently preserved in the

paleontology Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure ge ...

collections housed in the

Queensland Museum The Queensland Museum Kurilpa is the state museum of Queensland, funded by the government, and dedicated to natural history, cultural heritage, science and human achievement. The museum currently operates from its headquarters and general museu ...

, in

Brisbane Brisbane ( ; ) is the List of Australian capital cities, capital and largest city of the States and territories of Australia, state of Queensland and the list of cities in Australia by population, third-most populous city in Australia, with a ...

, Australia. ''Cratochelone'' was first studied by Herber A. Longman, husband of Irene Longman, of the Queensland Museum. Longman's 1915 type description of the genus and species was published in the '' Memoirs of the Queensland Museum''. The generic name was coined by Longman to be a contradistinction of the related Albian genus '' Notochelone'' also described from Queensland. The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''berneyi'' is in honor of F. L. Berney who recovered and donated the specimen to the museum. ''Cratochelone bernedi'' is one of three protostegid sea turtle taxa described from the fossil record of Australia. Described in 1885 '' Notochelone costata'' is the smallest species, while the most recently described species '' Bouliachelys suteri'', is between ''Notochelone'' and ''Cratochelone'' in size. In his type description Longman noted the incomplete nature of the fossil and hoped that more complete specimens would be found. Despite this, the type specimen remains the only known specimen of the species.

Description

The holotype specimen's forelimb is represented by the proximal ends of the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

and

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

. Though missing, the shaft of the humerus was similar to those found in primitive protostegid species. The wide angle of divergence between the scapular processes is similar to a number of early protostegid and cheloniids. The wide wings along the entoplastron and its lack of fusion with the surrounding bones indicates that Longman's placement of the genus is accurate. Longman noted the very large size of the bones, and estimated a complete specimen may have reached close to . This size was regarded as dubious by later researchers and was recorded several times as . Within his re-description of the type material in 2006, Benjamin Kear reaffirmed the size of full specimens to be in the range.

References

{{Testudines Early Cretaceous reptiles of Australia Protostegidae Early Cretaceous turtles Fossil taxa described in 1915 Prehistoric turtle genera Extinct turtles